"Given its direct influence over the separatists, Russia, and President Putin in particular, has direct responsibility to compel them to cooperate with the investigation," Obama said in a statement on Monday.

On CNBC's "Fast Money," Gartman offered three ways to trade the tension.

First, Gartman said to keep an eye on oil, and to use any rallies as opportunities to sell. According to Gartman, crude is likely to trade higher on initial headlines, but in the long-term could go as low as $85 a barrel.

Next, Gartman said that wheat prices, already down 21 percent in the past month, are likely to continue to slide. According to Gartman, Ukraine's increased wheat exports are driving prices lower. "Ukraine needs that money, and it has excess wheat with which to export," he said.

Finally, Gartman said that the U.S. bond market "wants to try to go higher" as traders seek quality amid an increasingly uncertain investment landscape. "Money is moving away from Europe and its moving to the United States, and it's going to park itself into debt securities," he said.